Attitude control apparatus for aircraft



Mardi 2, 1965 A. D. FORsBERG ETAL 3,171,616

ATTITUDE CONTROL APPARATUS FoR AIRCRAFT Filed Deo. 27, 1960 ask . craft.

United States Patent O 3,l7 1,616 ATTITUDE CONTROL APPARATUS FORAIRCRAFT Arthur D..Forsberg, Forest Lake, and Richard A. Verness,

Minneapolis, Minn., assignors to Honeywell lne., a corporation ofDelaware Filed Dec. 27, 19de, Ser. No. 78,750 12 Claims. (Cl. 24477)This invention relates to improvements in automatic control apparatussuch as automatic pilot systems for air- An automatic pilot system mayoperate attitude changing means of the craft such as a control surfacewith the surface alternatively being directly manually operated. Theinvention in more particular pertains to an automatic pilot systemhaving a trim control for altering attitude and 4an automatic flightpath control for maintaining a flight condition and wherein followingintroduction of the flight ,path control and subsequent operation of thetrim control, the flight path control is automatically disabled.

In an aircraft equipped with an automatic pilot of the type to bedescribed, the pilot may select a preengaged mode, an attitude holdmode, or a flight path control mode. During the disengaged mode, thepilot of the aircraft maymanually operate attitude changing means of-the'craft to place it in various attitudes, and the automatic ,pilotmeanwhile will be automatically or manually synchronized to the1attitude assumedby the aircraft. In the attitude hold mode, Aanattitude responsive device along with anpattitude selector or trimdevice may determine the attitude to be automatically maintained. ln theflight path mode when the flight path contemplated may be either thatderived from an altitude sensor, radio beam devices, or similar means,the aircraft will be guided to andthereafter maintain a positiondictated by the flight path sensor.

In the event thatthe autopilot trim control be operated while the flightpath mode is in effect, any command initiated from operation of the trimmeans tending to change attitude and deviate from the flight pathmamtamed 1s Vresisted by the ight path sensor. An extreme deviationwould have an unwanted effect on the flight path sensor 4such as anundesiredpitch up or down.

An object of this invention is tov-insure that a flight pathsensor ofthe automatic pilot is rendered ineffective upon operation of a trimcontrol of the automatic pilot.

. of a number of selected positions during a pilot operated mode of anautomatic pilot but during a flight path mode of the automatic pilot anypredetermined operation of v,the trim device will render the flight pathsensor ineffective=on the automatic pilot.

Afurther object of this invention is to provide an automatic pitch axiscontrol for an aircraft wherein said control includes a manuallyoperable trim control device v forselecting the operating point of thecontrol system and wherein thereafter altitude control may be introducedwhich is however automatically disabled upon subsequent operation of thetrim device a small predetermined extent.

The above objects and other novel features of this in- -.vention may bemore readily understood with reference Vvto the following descriptionand accompanying drawing of a preferred embodiment of the invention.

` In the drawing, the single gure discloses an electric einen PatentedMar. 2, 1965 ICC schematic of the trim adjusting-altitude controldisabling device.

Referring to the drawing, the invention is shown as being applied to anautomatic pilot for an aircraft which controls the pitch attitude of anaircraft through operation of attitude changing means such as anelevator surface lil. The pitch control surface 10 is operated from aservo lll which may be of the hydraulic type which in turn is controlledfrom an amplifier 12. The amplifier l2 may be of the A.C. discriminatortype and is supplied with A.C. control signal voltages derived from aDC. to AC. modulator 13 connected to a signal summing conductor ld of abalanceable DC. signal network i7. Depending upon the phase or polarityof the signal voltage on summing conductor ld, the servomotor ll willposition the control surfa lll in one direction or another.

The network i7 is illustrated as a parallel summing multiple DC. controlsignal summing arrangement. Multiple signals are supplied from varioussources comprising a pitch attitude signal potentiometer 18, a trimsignal providing means for signal potentiometer 2i), a pitch rate signalpotentiometer 22, an altitude displacement signal potentiometer 24, asynchronizing potentiometer 26, and an up-elevator potentiometerarrangement 2S. The potentiometer l is operated from a verticalgyroscope 19 in accordance with the pitch attitude of the aircraft. Thepotentiometer Ztl is operated from a manually operable trirn knob 2l.The potentiometer 22 is operated from a rate gyroscope 23 responsive topitch rate of the aircraft. The potentiometer Zd is operated through asuitable operating means 25 extendingfrom an altitude sensor 66, to bedescribed. Potentiometer Zd is operated from a synchronizer motorarrangement 3d, and potentiometer 28 is operated from a verticalgyroscope 29 in accordance with the roll attitude of the aircraft.

The potentiometers are conventionally energized from DC. supplyconductors 3l, 32 extending to a suitable DC. supply (not shown).

During what may be considered a pre-engaged mode for the automatic pilotsystem, the A.C. output of modulator i3 4is supplied to a discriminatoramplifier 35 in the synchronizer arrangement 34. The amplifier output issupplied to an amplifier phase winding 37 of `an induction motor 36lwhich has its Yother winding 38 connected through switch il when closedto an A.C. energized conductor eil. Energization of the motor 36 and itsconsequentv rotation is transmitted through gear train d2 and operatingtransmission means 27,to the attitude displacement error potentiometer26. During such pre-engaged mode, the control surface l@ may be manuallyoperv ated through suitable operating means such as. acontrol `stick i3connected through motion transmitting means i4 to the lelevator surface10. During changes of aircraft attitude incurred through the operationof the manually operable means` 43, any signal unbalance in summingconductor ld results in the operation ofthe synchronizer arrangement 3dwhich drives the potentiometer 26 to rebalance the network 17 and nullkthe signal on conductor lll.

During the transition to the engage mode `or attitude hold inode, whenthe automatic pilot controls elevator lll, DC. power yvoltage from asupply conductor 49 passes through a master switch 5t), a normallyclosed momentarily opened disengage switch 51, an autopilot kengageswitch 52, conductor S76, to an autopilot relay circuit 6l?. Theoperationof .the relay circuit 60 in well-known manner conditions orprepares the servornotor lll to operate the surface 10 by supplyingpressure fluid thereto. The autopilot engage switch 52 is of themanually closed solenoid held type and comprises a manually operableswitch arm 53 and a solenoid hold C9 arrangement 54 for maintaining theswitch in closed position after manual operation. Thus, upon manualoperation of switch 52 in a manner well known in the art to a closedcircuit position, and with the opening of switch 41, the attitude of theaircraft is maintained by vertical gyroscope 19 through the automaticpilot in accordance with the l'attitude of the aircraft attained uponoperation of switch 52.

An outer loop or flight path control in the form of altitude hold may beapplied to the network 1'7 by operation of an altitude engage switch 57which is also of the manually closed-solenoid held type similar toswitch 52. Closing of switch 57 at this time completes a circuit throughconductor 61, conductor 63 and valve operating solenoid 64 which effectsthe closing of a valve 65 of altitude sensor 66.

The altitude sensor 66 may be of the trapped air type and comprises acasing 67 supporting therein a diaphragm 69 of the resilient expansibletype. Pressure to the interior of diaphragm 69 is supplied throughpreviously open valve 65 from a static pressure supply line 68 connectedto the atmosphere. The interior of casing 67 and therefor the exteriorof diaphragm 69 receive static pressure through an opening 70 in casing67. With the valve 65 in open position, no differential pressure existson the diaphragm 69 since equal pressures are applied to the interiorand exterior thereof. However, upon closing of valve 65 at a selectedaltitude to be maintained by the aircraft and upon any changes inaltitude of the craft therefrom, a differential pressure exists ondiaphragm 69 causing movement of the output member 71 which is connectedthrough operating transmission means to the altitude displacement errorpotentiometer 24. Upon any subsequent reopening of valve 65, theresiliency in diaphragm 69 and the equalities in its interior andexterior pressures causes the potentiometer 24 to be recentered orreturned to the condition existing at the closing of switch 57 therebyrendering potentiometer 24 ineffective.

Coming now to the details which coact in a novel manner with the abovealtitude control apparatus, for disengaging altitude control there isassociated with the holding solenoid 59 of switch 57 a switchingarrangement 75 of the positively opened-self closing type. Thisswitching arrangement comprises two resilient operable arms 76, 77 withtheir respective coacting contacts 78, 79. An energizing circuit forholding solenoid winding 59 is provided with switch 57 closed andextends from energized conductor 61, conductor Sil, switch contact 79,switch arm 77, conductor 82, switch arm 76, switch contact 78, conductor81, solenoid winding 59, and thence to ground. Operatively associatedwith the altitude disy engage control switch arms 76, 77 is an altitudedisengage switch operating means 84. The switch operating means 84 iscarried by a driven clutch member 87 and is connected through a magneticclutch 85 when closed, and motion transmission means 90 to the operabletrim knob 21. The clutch 85 includes drive element 88 along with drivenelement 87 operatively connected to switch operating means 84. Thesolenoid clutch 85 is operated by magnetic clutch winding 89 which isenergized upon the closing of the altitude engage switch 57 being inparallel electrically with the winding 64- that' effects closing ofvalve 65 of altitude controller 66.

Upon subsequent operation of the trim knob 21 following closing of thealtitude engage switch 57 such operation of the trim knob 21 istransmitted through means 90 and clutch 85 to the switch arm 84 todisplace it. The switch arm 84 and the switching arrangement 75 areshown forrclarity in the drawing at right angles to their normaloperative position in the apparatus. The switch operating means 84 ispositioned intermediate switch arms 76, 77V and may be displaced toengage switch arm 76 when trim knob 21 is rotated in one direction andis displaced to engage switch arm 77 if trim knob 21 is rotated in theopposite direction. Upon engagement of operating arm 84 with eitherswitch arm 76, 77 the circuit through altitude engage switch solenoidhold winding 59 is opened, and the altitude engage switch arm 58automatically moves to open position. This opening of switch 57 opensthe circuit through magnetic clutch winding 89 and valve operatingsolenoid winding 64 rendering the altitude sensor 67 inelective onnetwork 17 and also as conventional opening clutch 85. There issufficient resiliency in either of the switch arms 76, 77 if operated todisengage its contact, so that upon opening of the clutch 85, therespective switch arm 76 or 77 will return to engagement with itsrespective contact 78 or 79 depending upon which switch arm has beendisplaced against the opposition of switch operator 84.

Summarizing the operation, in the pre-engaged mode when the aircraftattitude changing means 10 is being directly manually positioned fromcontrol stick 43, the engage switch 52 is in open position as shown andswitch 41 is closed. Any unbalance in D.C. summing network 17 derivedfrom operation of gyro 19 or other causes of imbalance in network 17 arerebalanced by operation of the synchronizing arrangement 34.

In the attitude hold or automatic pilot engaged mode, switch 52 is inclosed position and held therein by solenoid holding means 54 and switch41 is in an opened position. 1n the attitude hold mode with theautomatic pilot engaged, the aircraft attitude is maintained byoperation of the vertical gyro 19.

While in the engaged mode, flight path control may be introduced byoperation of the altitude engage switch 57 which energizes solenoid 64of valve 65 trapping air within diaphragm 69 at a given pressure. Anychanges in exterior pressure on diaphragm 69 from that existing at theclosing of valve 65 will result in operation of potentiometer 24 todevelop an altitude control signal which restores the aircraft so thatpressures on the diaphragm 69 are equalized. At the same time that valve65 is moved to the closed position, clutch operating winding 89 isenergized to operatively connect the switch operating means 84 to thetrim knob 21. Upon operation `of trim knob 21 subsequent to theintroduction of altitude hold by closing of switch 57, the switchoperating means 84 will be moved or displaced through a predetermineddistance depending on the spacing of ioperator 84 and arms 76, 77usually very small to `operate one or the other of switch arms 76, 77 toopen the circuit through the altitude engage switch holding solenoidwinding 59 thereby opening switch 57. Opening switch 57 opens thecircuit through valve operating winding 64 resulting in the valve 65automatically moving to open position. Opening switch 57 also causes thedeenergization of clutch operating winding 89 separating the clutchelements 87, 88 and causing the `operated switch arms 76 and 77 tore-engage its coacting contact.

After such subsequent operation of trim knob 21, the altitude engageswitch 57 may be operated again to restore altitude hold by closingvalve 65. Preferably there is no significant spacing between operator 84and switch arms 76, 77.

Although a separate motor operated synchronizing potentiometer 26 and aseparate manually operable trim potentiometer 20 have been illustrated,their functions may be combined in a single potentiometer by dispensingwith potentiometer 26 and extending the operating means 27 through aslip clutch to the motion transmission means 9i), the slip clutchpermitting operation of the manual trim knob '21 without interferencefrom the step down gear train 42.

It will now be apparent that there has been provided for an aircraftautomatic pilot having ia trim control arrangement for changing craftattitude and a constant altitude control, an interlock arrangementwhereby when constant altitude has been applied to the automatic pilotany attempt to operate the trim control to alter craft attitude, whereinsuch trim operation involves a predetermined displacement of the trimcontrol, and consequently cause indirectly a change yin altitude,altitude control is rendered ineffective on the automatic pilot, therebyenabling the trim control through the automatic pilot to alter craftattitude without oppositionfrom the altitude control. `It will also beapparent Athat such rendering the altitude control ineffective isaccomplished by an arrangement coupled to the trim means only afterinitiation ofthe altitude control whereby the trim means ymay beoperated independently ofthe altitude control priorto altitude controlintroduction.

We claim:

l. In control apparatus for altering the attitude of an aircraft, incombination: attitude responsive means; balanceable means, whereby craftattitude changing means may be positioned, operated by said attituderesponsive means; operable `further trim means affecting the balance ofsaid balanceable means; switch operating means; flight path maintainingmeans; selectively operable switching means operativelyr coupling saidflight path maintaining means to said balanceable means and alsoinitially coupling said switch operating'means to said further trimmeans for subsequent operation therewith; and flight path disengagingswitchingmeans Vconnected to the selectively operable switching means;and means operating said disengaging switching means by the switchoperating means upon subsequent operation 4of the further trim means tooperably decouple the flight path maintaining means from saidbalanceable means.

2. In control apparatus for a dirigible craft, in cornbination: attituderesponsive signal providing means; further signal providing means; aflight path sensor; flight path signal providing means; selectivelyoperable switching means enabling operation of the flight path sensorand the flight path signal providing means; switch operating means;additional means controlled by the selectively operable switching meansconnecting said switch operating means to said further means in anyloperated position thereof; means for combining the signals of the threesignal providing means; and positively opened-self closing disengagingswitching means controlling the selectively operable switching means andoperated to lopen position by the switoh operating means upon subsequentoperation of the further means to disable operation of the flight pathsensor and the flight path signal providing means.

3. In flight control apparatus for an aircraft Ihavin-g servo means ormanually operable means operating atti tud-e :changing means of thecraft to control attitude thereof, in combination: attitude responsivesignal providing means; attitude -command signal providing means;altitude disengage operating means; an altitude sensor; an altitudesignal providing means; selectively operable means rendering thealtitude sensor effective to displace the altitude signal providingmeans and si-multaneously initially connecting said altitude disengageoperating means to said attitude command means; means for combining thesi-gnals of the three signal providing means and controlling the servomeans; altitude disengage control means controlling the selectivelyoperable means; and means operating the altitude disengaging controlmeans by the altitude disengage operating means upon subsequentoperation of the attitude command means to render the altitude sensorineffective on the altitude signal providing means to prevent thealtitude sensor opposing changes in attitude derived from operation ofthe attitude command means.

4. In flight control apparatus for an aircraft having a control surfaceand 'servo means or manually operable means operating the same forchanging craft attitude, in combination: pitch -atti-tude signalproviding means; pitch trim signal providing means normally disconnectedfrom the trim signal providing means; switch operating means; a flightpath -sensor signal providing means; selectively operable meansoperatively connecting said switch operating means to said pitch trimmeans in any position vthereof for subsequent `movement therewith; meanscombining the signals of the three signal providing means andcontrolling said servo means; flight path disengaging switching meanscontrolling :the selectively 'operable means and actuated by the switchoperating means upon such subsequent operation of the pitch trim meansto render the flight path sensor signal providing means ineffective tocontrol the servo means whereby trim change of the craft may be effected:Wit-hout opposition |from the lflight path sensor.

5. In flight control apparatus lfor a diri-gible craft having attitudevchanging means thereon and servo means and manually operable meansoperating .said attitude changing means, in combinati-on: balanceablemeans operating said servo means; further means including motor operatedsynchronizing means effecting-the balance of said balanceable means;switch operating means; flight path maintaining means; `selectivelyoperable switching means rendering said flight path maintaining meanseffec- Htive on said balanceable means, disabling said synchronizingmeans, and `initially coupling said switchoperating means to saidfurther meansfor subsequent operation therewith; and flight pathdisengaging switching means connected to Ithe selectively operableswitching means and operated by the switch operating means uponsubsequent operation of the further means -to render the flight pathmaintaining means ineffective on said balanceable means.

6. In navigating apparatus for an aircraft, in combination:attitude-sensing variable magnitude signal providing means; craft trimvariable magnitude signal providing means; flight path sensing means; anadditional variable lmagnitude signal providing means; selectivelyoperable `switching means to enable said flight path sensing means tooperate said additional signal providing means; signal responsive meanscontrolled by said three signal providing means and having an output inaccordance with which the craft may be controlled; switch operatingmeans; means now initia'lly coupling said switch operating means to saidtrim signal providing means, for subsequent operation therewith, inresponse to operation of the selectively operable switching means; andmeans including a normally closed-momentarily opened disengagingswitching means controlling the selectively operable switching means andtemporarily moved to the open position by the switch operating means todisable the flight path sensor upon subsequent small operation of thetrim signal providing means to operate said additional signal providingmeans.k

7. In -control apparatus for an aircraft having attitude changing meansoperated either by servo means or by manual means, in combinati-on:attitude sensing variable signal voltage providing means; a variablypositioned .trim signal voltage providing means; a flight path sensor; afurther variable signal voltage providing means; control means for saidservo means responsive initially during variations of the signals fromthe first two signal providing means but subsequently responsive duringvariations to said three signal voltage providing means; a switchactuator; selective means rendering said flight path sensor effective-on said further signal providing means for operation thereof for suchsubsequent response of the control means and coupling said switchactuator to said vtrim signal voltage providing means so that onsubsequent additional positioning of the trim signal providing meanssaid switch actuator moves through a constant additional displacement toengage .the selective means .to render the flight path sensorineffective on said further signal providing means to prevent a steadystate signal therefrom opposing change in trim.

8. In control apparatus for an aircraft havin-g attitude changing meansoperated either yby servo means or by manual means, in combination:attitude sensing variable magnitude signal providing means; a variablydisplaceable variable Imagnitude trim signal providing means; a

flight path variable magnitude signal providing means;

control means for said servo means responsive to variations in signalsfrom said Ithree signal providing means; and means selectively coupledor uncoupled to said t-rim signal means so that on subsequent additionalconstant displacement of the trim signal providing means said flightpath sensor is rendered ineffective, to enable change in trim Withoutopposition by said flight path signal means.

9. The apparatus of claim l8, and synchronizing means 'responsive tosaid control means during manual operation of the attitude lchangingmeans to null said control means for attitude changes of the craftduring such manual control.

10. In control apparatus for an aircraft having attitude changing meansoperated by servo means, in combination: attitude sensing signalproviding means; trim signal providing mean-s; flight path sensor signalprovid- -ing means; control means for said servo means responsive tothethree signals from said s-ignal providing means;

f tions thereof; operable aircraft tri-m means; signal means responsiveto the first flight condition sensing means and aircraft trim means; asecond flight rcondition variation ksignal providing means andcontrolling the flight path sensing means; means selectivelyl renderingsaid signal means also responsive to variations affecting said secondflight condition sensing means; and means thereafter effective onlyfollowing such selection of the -signa'l means whereby it responds tovariationsin the second flight condition means and additionally on afurther but constant additional extent of operation `of said trim meansrendering the second flight condition sensing means ineffective on saidsignal means, to prevent opposition to Ichange in trim by the secondilight condition sensing means.

l2. In control apparatus for an aircraft having attitude .changing meansoperated by manual or by servo `means, in combination: balanceable meanscontrolling said servo means; means including a manually operable trimmeans connected to the balanceable Imeans and operated to a position toselect an attitude to be maintained; flight path sensing means;selectively operable means Arendering said flight path sensing meanseffective on said balanceable means; and means -elfective on subsequentlfurther operation of said trim means from its attitude select lpositionrendering said flight path sensing means inoperative on said balanoeablemeans to prevent opposition -to change in trim by said flight pathsensing means. l

References Cited by the Examiner UNITED STATES PATENTS 2/59l Owen 244-772/60 Seliger 244-77 FERGUS S. MIDDLETON, Primary Examiner.

MILTON BUCHLER, Examiner.

1. IN CONTROL APPARATUS FOR ALTERING THE ATTITUDE OF AN AIRCRAFT, INCOMBINATION: ATTITUDE RESPONSIVE MEANS; BALANCEABLE MEANS, WHEREBY CRAFTATTITUDE CHANGING MEANS MAY BE POSITIONED, OPERATED BY SAID ATTITUDERESPONSIVE MEANS; OPERABLE FURTHER TRIM MEANS AFFECTING THE BALANCE OFSAID BALANCEABLE MEANS; SWITCH OPERATING MEANS; FLIGHT PATH MAINTAININGMEANS; SELECTIVELY OPERABLE SWITCHING MEANS OPERATIVELY COUPLING SAIDFLIGHT PATH MAINTAINING MEANS TO SAID BALANCEABLE MEANS AND ALSOINITIALLY COU-